Magnetized sewing needles



May 26, 1970 D. R. DOHR MAGNETIZED SEWING NEEDLES Filed Sept. l0, 1968 Fig. 6

INVENTOR.

R. Dohr Donald United States Patent O 3,513,793 MAGNETIZED SEWING NEEDLES Donald R. Dohr, Bloomfield, NJ., assignor to rI he Singer Company, New York, N.Y., a corporation of New Jersey Filed Sept. 10, 1968, Ser. No. 758,906 Int. Cl. Db 85/00 U.S. Cl. 112-222 5 Claims ABSTRACT 0F THE DISCLOSURE SUMMARY This invention relates to the art of sewing machines and more particularly to a novel and improved sewing needle for use therewith, whereby operator dexterity is substantially reduced in the steps normally required for the insertion and removal either of one or two such needles, and there is a substantial decrease in the possibility of dropping the needle through thethroat plate hole into the internal mechanism of the sewing machine.

The present invention comprises a sewing needle formed from a substantially permanent magnetic material, that is, a needle preferably composed of a hardened high carbon steel, which has aA magnetically hard state, `or in other words the steel is substantially vmore difficult to magnetize, but resists -demagnetization signiiicantly more so'than those needles formed of a soft magnetic material having a low carbonlcontent. Because of the magnetic properties of the needle, there is develv oped an attractive force between the needle and the nickel plated steel needle bar in which the needle normally is operatively disposed. Because of the geometry ofthe needle bar slot, contrary to `general applications Iwherein there exists a closed magnetic circuit (that is, no air gap exists) so that the breakaway force is inthe direction vof the ux vector, the predominant holdingfo'rce inv the needle-needle bar application comprises the frictional force at the needle-needle bar contact surface which is normal to the ux vector fand the magnetic attractive force. Further, it has been found that by Aplating lthe needle with aV thin layer`of material, such as gold, that the force required to withdraw the needle from the needle bar was increased substantially. One :would normally expect that the effect of the gold plating thickness would be to decrease the withdrawal force ofthe-needle, because the nonferromagnetic gap between the magnetized steel needle and-theneedle bar would be increasedby the thickness of the gold plating, and since the attractive magnetic holding force decreases inversely with the square of this gap, an accompanying decrease in holding force would be expected. However, in the present invention, the layer of gold acted as a multiplying factor of `the magnetic holding force. This unexpected phenomenon is attributed to a higher static coeicient of friction of the ducing no adverse effect on the magnetic holding force of the needle. In addition to the foregoing, the gold plating further provides an aesthetically desirable product with a noncorrosive outer layer, as well as a more readily visible thread-receiving needle eye.

Accordingly, it is a principle `object of the present invention to provide an improved type of needle for use in a sewing machine, which substantially reduces operator dexterity normally required in the insertion of one or more needles into the needle bar or the removal l.of one or more needles therefrom. .A f l Another object of the present invention is to provide a magnetized needle which remains magnetically strong for its intended purpose.`

A further object of this invention is to provide for use in a sewing machine, a plated magnetized needle which provides a significant increase in the withdrawal force required for removal thereof from the needle bar.'

A still yet further object of the present invention is to provide a plated magnetized sewing needle which combines highly desirable magnetic characteristics thereof with increased wear resistance and easier threading.

Having in mind the above and other objects that will be evident from an understanding of the disclosure, the invention is illustrated and described in the presently preferred embodiment thereof which is hereinafter set forth in such detail as to enable those skilled in the art readily to understand the function, operation, construction and advantages of it when read in conjunction With the accompanying drawing in which:

BRIEF DESCRIPTION OF THE DRAWING 4with the present invention;

FIG. 3 illustrates an enlarged elevational view of a sewing needle constructed in accordance with the present invention, thelines indicating the magnetic iield develgold on the surface of the needlel bar compared to that y of nickel, the normal needle plating. To increase the hardness of the gold, approximately 0.2 percent cobalt was used with pure gold. This composition was found to substantially double the hardness of the gold, while prooped lby the needle;

FIG. 4illustrates a vertical sectional view of the needle disposed in the needle bar substantially taken onthe line 4--4 of FIG. 1, the lines indicating the magnetic field developed by the needle relative to the needle bar;

FIG. 5 illustrates a vertical sectional view substantially taken on the line`5-5 of FIG. 4, the lines indicating the magnetic field developed by the'needle relative to the needle'bar; and i FIG. 6 killustrates a cross-sectional View substantially taken on the line 6,-6 of FIG. 5, thev lines indicating the vmagnetic field developed by'the needleV relativesto the adjacent needle bar surface.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring more' specifically to the drawings, wherein like reference numerals denote similar parts throughout the various views, the preferred embodiment of the present invention is herein disclosed for use in a sewing Inachine, for example, substantially like that forming the subject matter of U.S. Pat. No. 2,920,593 assigned to the assignee of the present invention. However, lit is to be understood and it will be readily apparent from the following specilication that the sewing needle comprising the present invention is not limited to use with any particular sewing machine or needle carrying needle bar. The present specification describes only those parts of the sewing machine necessary for a complete and accurate understanding of the present invention.

In FIG. 1 there is disclosed a sewing machine comprising the usual frame structure including a head overhanging the portion of the bed (not shown) mounting a throat plate 11 provided with the usual needle receiving throat plate hole 12. In the head of the machine there is mounted for endwise reciprocation and sidewise movement a cylindrical needle bar 13 having a needle generally referred to by the numeral 14, to be described in detail hereinafter, secured at its lower end by a standard needle clamp 15, such as that forming the subject matter of a U.S. Pat. No. 2,973,733 assigned to the assignee of the present invention, to which reference may be had for a more complete description thereof.

More specically, as best shown in FIGS. 4 and 5 the `lower end of the needle bar 13 is formed with a vertically vflat walls 18 and 19. The needle clamp 15 comprises a clamping band 20 which surrounds the lower portion of the needle -bar and is formed with a bore 21 for slidingly receiving the needle-bar 13. A boss portion 22 depending from the band 20 is provided with a threaded bore 23 into which is secured a thumb screw 24 whose inner end portion has a conical shape 25. A screw 26 rmly secures the needle clamp band 20 to the needle bar 13 as shown in FIG. 5.

FIG. 2 illustrates the foregoing described needle clamp accommodating two needles 14-14 instead of the single needle disclosed in FIGS. l and 3-6, inclusive.

The needle clamp or for that matter any other suitable needle clamp is adapted to receive the sewing needle 14 illustrated as having a shank portion 27 formed as a slab-sided circular cylinder with the slabbed side 28 being disposed on the opposite side of the needle from the usual elongated groove 29 formed in the blade 33 of the needle, the usual thread-receiving eye 34 and needle point 35. As more fully described in U.S. Pat. No. 2,973,733 the needle properly is located in the needle-shank receiving yslot 16 with the slabbed side 28 of the needle 14 disposed adjacent the at wall 18 of the needle bar 13 as shown in FIG. 6. With the needle in this position the operator then may advance the thumb screw 24 so that the conical head 25 will engage a peripheral rounded Wall of the needle thereby forcing the needle shank 27 into the pocket or seat formed by the angularly disposed walls 18 and 19. A continuously arising problem is that oftentimes the operator finds it diflicult to locate the needle properly in the needle clamp and is apt to loose his grasp on the needle and it will fall onto the surface below and possibly through the throat plate hole 12 into the internal working mechanism of the sewing machine. The dexterity of the operator is particularly important when two such needles are used for sewing as shown in FIG. 2.

FIGS. 4 and 5 show that the needle is located at the proper height within the needle bar 13 by means of the screw 26 which serves as an abutment stop for the needle as it is inserted upwardly into the slot 16.

The presently disclosed needle obviates the foregoing discussed problems found with conventional sewing needles and is unique in that it is magnetized and is formed with a thickness of gold plating over its surface. It is to be understood from the outset that it is not the purpose of this specification to discuss in detail the theory of magnetism and reference is made to a textbook such as Magnetic Circuits and Transformers prepared by the Department of electrical Engineering at M.I.T., John Wiley and Sons, Inc. for a detailed analysis and discussion thereof. As best illustrated in FIG. 6, the needle 14 comprises a steel main body portion 30, the usual layer of nickel plating 31 found on conventional needles, and an outer layer of gold designed by the numeral 32. As mentioned before, preferably the needle is of the hardened high carbon content variety. Among the advantages of providing the needle with a layer of gold are that it enhances the needle appearance aesthetically, provides better visibility for threading, increases the wear resistance of the needle and most importantly, increases the needle bar holding force for the magnetized sewing needle.

By using a suitable plating process, which is not within the scope of the present invention, the layer of gold can be applied to sewing needles of any variety. The gold plating process consists essentially of cathodically cleaning the needle surface, activating the previous nickel plating and the gold plating. The gold'plating preferably comprises an alloy (nominally v99.8 wt. percent Au, 0.2 wt. percent Co) with significantly higher inherent hardness than pure gold (140-200 Knoop compared to 70- This gold composition has excellent adhesion to the nickel substrate plate and in combination with the inherent hardness of the plate, a minimum plating thickness of approximately 20 microin'ches provides adequate Wear resistance for normal needle life.

It has been learned that by gold plating a sewing needle and subsequently magnetizing it the force required to withdraw the needle from the needle bar is increased by up to 40 percent. This phenomenon is believed due to the higher static coefficient of friction of the gold plating on the machined-steel surfaces of the needle bar compared to that of a conventional nickel-plated needle. This also was found to be true for the nickel-plated, casehardened needle bars as well as for chromium-plated cold-finished steel needle bars. For example, experimental tests show that gold has a static coefficient of friction of 1.2 against nickel plated steel While that of a nickelplated needle was found to be 0.73 against the same needie bar. With the gold-plated magnetized needle placed loose in the needle bar the withdrawal force (FW) required to break the magnetic attraction of the needle to the needle bar is affected by the static coefficient of friction (,u) 0f the needle surface 28 against the machined steel or plated surface 18 of the needle bar 13. This force (FW) is the product of the static eoeicient of friction (,u) and the normal magnetic attractive force (Fn) or in other terms, FW=p.F. Thus, it is conceivable to experience a withdrawal force (FW) higher in magnitude than that of the attractive magnetic force (Fn) if the two contacting materials have surfaces which give a coefficient of friction greater than one. In the present invention, with the gold acting as a multiplying factor, the force required to withdraw the needle from the needle bar was greater than the force of gravity on the needle per se and therefore, the magnetic attractive force was suicient to hold the needle in place. The use of materials other than gold to alter the attractive force Fn is Within the scope of the present invention provided the coefficient of friction is such that the withdrawal force is greater than the :torce of gravity on the needle. The attractive or normal force Fn is defined by the equation.

and the needle bar in gauss, and

Alg-:area of the gap between the needle and the needle in dynes l bar in cm?.

As mentioned above, the needle 14 is held in the needle bar 13 primarily by a magnetic force wherein the magnetic force between the permanent magnet needle and the substantially flat wall 18 of the needle bar slot 16 holds the slab side 28 of the needle shank 27 against the needle bar wall 18, as best shown in FIG. 4.

. To establish a magnetic circuit such as that illustrated by the magnetic flux distribution in FIG. 3, a suitable procedure for magnetizing the needle was chosen. Although there are numerous methods, such as the use of a Permanent Magnet Magnetizer, Direct Current Magnetizer,

Haly-Cycle Magnetizer, to attain the desired result, the preferred approach comprisesusing a condenser d1scharge type magnet charger of the Radio Frequency Laboratory type' (Model 107A), which operates on the principleof storing energy in a capacitor over a period of time (at mostf several seconds) and then discharging the stored energy through an appropriate fixture, such as a coil, inV a relatively short time, i.e., several milliseconds. Such units are powered from 115 v., 50-60 cycles/sec. single phase lines. This method is advantageous in that the coil can be placed around a conveyor belt,VV for example, and electronically operated, thus, being very suitable for mass production. Further, the needles to be magnetized can be oriented in a controlled manner with respect to the magnetic field. One approach would be to magnetize individual boxes of needle cards.

It is known thatto magnetizek an article such as a needle, an external field has to be applied so that the ferromagnetic domains of the material reorient from a random orientation Withrespect totheapplied field and contribute additional ux, thus amplifying `the magnetic ux present due to the externally applied field force alone. Once this change has been produced it is important that resultant magnetized article not.- reverse back to its original state. Thus, to obtain apermanently magnetized needle a crystal structure which effects a resistance to change in the magnetic stateis essential. The ability of a material to arrange the orientation of its atoms such that their magnetic moments are at a'maximum is known as the ferromagnetic property of that material. This property varies with the crystallographic structure of the material and its state of internal energy or stress. For example, quenching of high carbon steel, tot form martensite which makes up the major portion of the present needle composition, produces the desired resistance to change of magnetic state. In other words the resultant martensitic crystal structure resists demagnetization moreso than other allotropic crystallographic structures of the needle steel. Substantially permanent magnetization of high carbon steel requires a magnetizing field of substantially 6100 ampere-turns/in. (300 oersteds) for saturation. Material of this type to be demagnetized must be subjected to a large externally applied field of opposite sense to lower its residual flux density, that is, the flux density remaining (Br, remanence) when the applied field is removed. The measure of the permanence of the materials ferromagnetic property is the demagnetizing field necessary to reduce the magnetic flux density (Br) to zero and is defined as the coercive force.

Thus, a magnetic induction in gauss is induced in the needle when an external DC or pulsed magnetic field of predetermined strength is applied. On removing the needle from the magnetic field, a residual magnetic induction (Br), or some fraction thereof, remains in the needle. When the magnetized needle is brought close to a separate magnetic field of opposite sense or touches an initially unmagnetized, magnetically soft or hard material such as the needle bar, then the residual mag-netic induction is further decreased until it attains an equilibrium position with the opposing field or with the magnetically soft or hard part. Subsequent introduction of the needle to these same conditions Will reduce the magnetic force a minimal amount only. Therefore, for all practical purposes, it has attained an equilibrium condition. Its magnetized state will change only if brought into contact with a larger field.

In magnetizing the gold plated needles it is preferable to do so after packaging of the needles, since if they were magnetized first the needles would stick together and make packaging most difcult.

Also, it is preferable to magnetize the needles axially, i.e., with the external magnetic field applied coincident to the axis of the needle, rather than in a direction perpendicular to its axis (that is, cross magnetized) in order to obtain the greatest possible force (Fw) required for withdrawal of the needle from the needle bar. By magnetizing the needle axially it appears that the path followed by the lines of ux, generally designated B, emerging from one pole of the needle into lthe air wherey the' opposition to the passage of the flux lines is very highl (permeability of air being unity) and back into the other pole thus completing the magnetic circuit, is much shorter than for a crossmagnetized needle. Thus, in the case of a cross-magnetized needle thelength'of the needle shank becomes apole and there exists a very short magnet with poles of large area resulting, therefore, in a very large .reluctance path or in other words, .path or resistance, for the tiux lines, thus reducing the holding. forceof the' magnet. Further, the reluctance of the magnetic circuit may effect the value of Bg as it may contain areas where ii-ux leakage occurs thus reducing its value. This indicates, therefore, that when the needles .are -initially magnetized, the magnetically stronger needle will be the one whose direction of magnetization favors the path of least resistance (reluctance) for the magnetic circuit, namely in the axial direction. For the same strength of magnetic induced field, the needle .with t-he lower reluctance path will have a higher Yresidual change in the cross section of the needle has on the flux density is readily apparent in this figure. Thus the needle 'shank portion 27, which has the largest cross sectional area of the needle will naturallyhave the largest number of fiux lines. Since the flux density is an intrinsicproperty of the needle material it remains constant throughout the needle per se. The flux density of the needle in air, however, is much lower than when the needle is inserted into a needle bar. This results from the fact that in the former the lines of fiux follow a path of high reluctance with a consequent decrease of magnemotive force (mmf). In the latter case the high permeability of the needle bar material results in a low reluctance path with a consequent increase in the mmf.

FIGS. 4, 5 and 6 illustrate a typical fiux distribution after the magnetized needle of FIG. 3 has been inserted into the needle bar slot 16. The greatest concentration of liux lines appears at the interface denoted A between the slabbed side 28 of the needle 14 and the flat wall 18 of the needle bar. Thus with the needle magnetized axially and in place in the needle bar, the lines of ux predominantly take the path of lowest reluctance which is through the steel at the tip of the needle shank at the needle-needle bar interface. The fiux density is highest `at and in the vicinity of the pole and decreases rapidly along the slabbed side 28 of the needle butt as it approaches the neutral magnetic axis in the shank of the needle.

Consideration must also be given to the nonferromagnetic gap, Ag, since the attractive force, Pn, is a function thereof. The eect of the area of the gap is minor when the gap is very small (approximately .002), because then the area essentially is the area of contact of the slabbed surface 28 of the needle shank 27. As the machined surface of the needle shank rests substantially against the needle bar surface at A, the gap is essentially very small in this area and the overall effect of the area is minor when compared to the flux density.

The attractive or normal force, Fn, can be calculated from the above formula or alternatively can be measured with a suitable instrument. If the formula is used the air gap area, Ag, between the needle and the needle bar surfaces must be accurately determined. Once the force Fn is known the Withdrawal force, Fw, can be determined by multiplying lt, the coefiicient of friction of the material (gold) comprising the needles outer surface relative to the surface of the needle bar, by the force Fn. It can be seen that the withdrawal force, FW, is a direct function of both the coeicient of friction, n, and the ux density, Bgz. Therefore, when the coeicient of friction significantly increases the withdrawal force to a point where the mag- -netic force will hold the sewing needle in` theinee'dle'fbar as correspondingly'increasedto the qdesiredholding value to produce the results ofthe present invention.. J

It is to be understood that the present disclosure relates to a preferred embodiment of lthe invention, which is for purposes ofV illustration only, and is not to be construed as a limitation ofthefinvention. All such modifications which do not depart from the spirit ofthe invention are intended to be includedwithin thescolpe thereof.

. Having `thus set`V forth the' natureo'fz'this` invention, what is claimedghei'einv is` as followsz' l.

1. A. sewing needle lforen-sewing .machinefhaving va frame and sa needle-carrying@ferromagnetic)needle'bar mounted in said ,frame yfor. endwise ,reciprocatiom 'said needle ,bar vbeing provided .with la slot fadapted. for re.-

ceiving aportion of the needle therein; saidvneedle comprising ;a shank yportion adaptedrfto be disposed in "said slot, and being magnetized, at least the shank portion; of

said needle being coatedfwith a layer of' material, said magnetizred needle developing a magnetic e'ld which when the needle shank is placed in theLneedle-barfreceiving Vslot will have amagnetic'A attractive force disposed normal relative to anv adjacent "surface 'of the needle bar, said layer of material having when the needle shank is placed in the needle ibar receiving slot a coeicent of friction relative to an adjacent needle bar surface whereby there will be developed a combined magnetic-frictional retaining force requiring a force to withdraw the needle from the needle bar of a magnitude 8, 'greater than the force Aof gravity on the sewing vneedle'.

2.- In vthe sewing needle set forth inclaim 1, wherein the-layer of material comprises an alloy of substantially 99.8 percentvgold and O Zpercentcobalt` v 3. In the sewing needle set forth in claim 1 wherein the entire needle is provided Awith a layer of gold.

4. A :sewing needle including a shank portion and a vblade portion, said sewing needle being magnetized for developing a magnetic lield of predetermined flux density to product a resultant magnetic attractive force vector, atleast the shank portion of said needle having a layer of material disposed thereabout for substantially increas- ,ing the `:normal magnetic attractive .force developed by said. magnetizedsewing needle when brought into proximity,` with another ferromagnetic material.v

5. A sewing needle accordingto claim 4 wherein said material comprises anv alloy composed primarily of gold.

References Cited i UNITED STATES PATENTS 11,769 10/1854 .Wilcox et a1. 223-102 2,365,376, 12/,1958 Pellieret a1 22a- 102x FOREIGN PATENTS U.S. Cl. X.R. 

